Marine macroalgae, also known as seaweeds, remain largely unfamiliar to much of society despite their ecological and economic importance. This brief article highlights their significance, since only by knowing and valuing them can we recognize the need for their sustainable exploitation and conservation.

Ecological Role and Benefits. Marine macroalgae form undersea beds and forests that play essential roles in the functioning of coastal ecosystems and in structuring marine habitats. As primary producers, they contribute greatly to primary production, seawater oxygenation, inorganic nutrient cycling, and carbon storage, acting as important carbon sinks.

Their ecological relevance also extends globally, as macroalgal forests are among the most extensive and productive coastal vegetated ecosystems on the planet, with estimated net primary production comparable to that of the Amazon rainforest.

The macroalgae that form these beds and forests also act as ecosystem engineers and foundation species, providing habitat, shelter, nursery grounds, food, and foraging areas for many marine organisms of ecological importance and commercial value. They not only feed herbivores and omnivores directly, but also provide essential food for detritivores and suspension feeders in the form of detritus (i.e., small particles of decomposed organic matter derived from their tissues). Macroalgal forests also help protect coastlines by stabilizing sediments and reducing wave energy, thereby limiting shoreline erosion.

These ecosystem services have substantial annual economic value. For major kelp forest-forming species alone, fisheries production supported by kelp forest habitats, nutrient cycling, and carbon removal have together been valued at around US$500 billion per year.

Applications and Economic Value. Marine macroalgae are valuable marine resources used in many commercial applications and everyday products. One of their oldest and best-known uses is the direct consumption of edible species in East Asia, where seaweeds are valued for their flavor, high nutritional value, and health-promoting bioactive compounds. In recent years, seaweeds have also gained popularity as food in the West, where their role remains more limited, although demand is growing rapidly.

Less visible, but far more widespread, are the seaweed-derived compounds used across many industries. The most commercially important are macroalgal hydrocolloids, known as phycocolloids, which support a major seaweed-based industry. These phycocolloids are cell-wall polysaccharides and include alginates from brown macroalgae, as well as agar and carrageenans from red macroalgae. They are widely used as gelling, thickening, stabilizing, and encapsulating agents in food and beverages, textiles, paper, pharmaceuticals, biotechnology, biomaterial development, and other industrial products. Bioactive compounds from seaweeds are also used in medicine, cosmetics, and health-related products. Overall, these applications are so common that it is difficult to go through a day without using at least one product that depends on them.

Furthermore, marine macroalgae are used in livestock and aquaculture feeds, as agricultural fertilizers, and, more recently, as plant biostimulants. Beyond these established applications, they are also being explored for several emerging uses, including biofuels, the formulation of more sustainable fish feeds for aquaculture, and ruminant feed additives to reduce methane emissions.

To meet global demand for these uses, around 36.5 million tonnes of seaweeds are currently produced each year, with an estimated annual value of about US$17 billion. This makes seaweed production commercially significant, although this market value represents only about 4% of the estimated economic value of the three key ecosystem services outlined above.

Sustainable Exploitation and Conservation. The production of marine macroalgae has grown steadily, with an average annual increase of around 7%. This rate is much higher than that of other major sectors, such as agriculture, livestock, and fisheries, which have grown by about 2%, 3%, and 0.1% per year, respectively. This rapid growth reflects the increasing importance of seaweeds and the strong demand for their many uses, some of which are already part of everyday life. This demand is expected to continue increasing. Seaweeds are widely seen as valuable resources for the future, with potential applications in food, medicine, animal feed, and other essential products.

Today, most seaweeds used worldwide are produced through aquaculture in East Asia, whereas in the West, wild populations are still the main source. This dependence on natural resources in many Western countries is a growing concern, as many macroalgal communities are already declining due to climate change and other human pressures, including harvesting. This is especially important because their environmental value may be much greater than their direct commercial value. For this reason, the development of seaweed farming in the West is essential to increase production while reducing pressure on wild populations. Seaweed farming could also provide important environmental benefits. As a form of marine agriculture, seaweed farming can help make animal aquaculture more sustainable by recycling part of the inorganic nutrients (nitrate, ammonium, and phosphate) released by species such as fish and mussels.

César Peteiro

Tenured Scientist (permanent position) affiliated with the Department of Aquaculture and Blue Biotechnology at the Oceanographic Centre of Santander (COST), which belongs to the Spanish Institute of Oceanography (IEO), part of the Spanish National Research Council (CSIC).
His academic background includes a Bachelor of Science in Biology, a Diploma of Advanced Studies in Environmental Biology from the University of A Coruña (UDC), and a PhD from Rey Juan Carlos University (URJC). His doctoral thesis was entitled Open-sea cultivation of commercial kelps on the Atlantic coast of southern Europe.
He has more than 20 years of research experience in marine macroalgae (also known as seaweeds) addressing both fundamental and applied aspects through culture and experimentation. His work focuses particularly on the cultivation and conservation of kelp species (i.e. Laminariales and closely related orders). He leads the research group “Marine Macroalgae Cultivation and Experimentation,” whose main objective is to research, develop and transfer knowledge on the cultivation, sustainable use and conservation of seaweeds.
His research has contributed to the generation of original and relevant knowledge in the field of marine macroalgae, with a particularly significant contribution to kelp biology and aquaculture. His results have been published mainly in international journals with scientific and technological impact, including 30 publications indexed in Web of Science (WoS). Further details on his publications and research outputs are available through his institutional CSIC author profile (https://digital.csic.es/cris/rp/rp14639) and ORCID profile (http://orcid.org/0000-0003-0698-3573).